Wood screw



F H WILLIAMS wool) SCREW F 1 d M y 1921 Inventor W .23

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Patented Nov. 15, 1927.

STATES PATENT OFHQE.

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W'QQIID SCREW.

Application filed my 9, 1921. Serial No. 4%,808.

My" invention relates generally to screws and more particularly to screws which are designed to be driven into solid wood.-

For convenience-I have illustrated and described my invention as applied to railroad spikes, but it is. to be understood that it relates generally to all types of screws having the characteristic above stated.

it is well mown to those skilled in the art to that, when larger than a certain critical size,

' a square, straight spike has an increased pull and increased life of holding power, when 1t is driven into a properly proportioned and reviously drilled hole instead of being it orced directl cause for this 1s the fact that the wood fibers are deformed within, or not greatly in excess of, their elastic limit. The spike is, therefore, held within the wood by live fibers inno stead of by dead ones, formerly produced by driving a spike into the solid wood. As is well known, this latter method crushes, beyond their elastic limit, and breaks the fibers and thereby greatly reduces .the pull at and holding power, of the spike.

The chief object of my invention has been 'to provide a screw of such formation that it may be driven into solid wood. without materially splitting or crushing the wood or dis to torting the fibers beyond their elastic'limits,

while maintaining the desired resistance to withdrawal.

With this'in mind, I have provided a screw which is so formed that it causes only a coman paratively small displacement of the fibers of the wood into which it is driven.

My screw also presents a large surface area in contact with the wood, thus increasing its resistance to pulls and substantially maintainingsuch resistance durin the full life of'the wood into which it is driven. This resistance is still further increased by the spiral disposition of this surface area.

While preserving the foregoing charactertt istics'and advantages of to screw, 1 have so formed it that it has a gra ual or concurrent increase of transverse strength from a point, where the transverse strain on it is at a minimum up to apoint at or near the surface at of the wood when this transverse strain reaches its maximum.

The above objects and advantages have been accomplished by the device shown in the accompanying drawings, of which:

into the. solid wood. The

higfl is a; side elevation of a complete spike embodymg my invention.

Fig.2 is a longitudinal, sectional elevation of the spike, showing it driveninto a crosstie, and is taken on line 2-'2-of Fig. 3.

. Fig. '3 is an enlarged, transverse, sectional view of the spike taken on line 33'of Fig. 1.

Fig. 4 is a similar view online H of l. 1g: 5 Fig. 1.

The spike'comprises'a core 5 having a plurallty of spirally arranged threadsor projections 6, formed by flutes 7. The diameter of the core and the number and shape of. the threads. are such that when the spike is driven'into solid wood it will not materially crush the woodor distort the wood fibers beyond their elastic limits. By the term core, ll mean that portion of the spike con-- tained within the cylinder which is tangent to the bottom of the flutes 7. The threads 6 start .at a point on the spike which is substantially at or slightly below the surface of is a similar view on line 5-5 of the crossetie, and .they terminate near the be of any suitable pitch, it being necessary,

however, that the pitch be such that the spike will be rotated by an axial movement as it I is being driven into the wood. The flutes 7 at the lower ends of the threads are deepened as shown in Fig. 2

The core 5 is provided with a conical point 9. This point preferably extends below the lower ends 10 of the threads 6, and it serves to start a hole in the wood into which the spike is driven. The deepened, lower ends of the flutes 7 start at substantially the point where the upper end of the conical point stops. The core 5 is joined to the neck 11 of the spike by means of a tapered portion 12., This tapered ortion starts ata point on the core about mi way its length, which is where bending resulting from lateral pressure caused by the rail base practically ceases, and it extends u wardl to a point where it merges with t e nec 11 at or slightly below the surface of the cross-tie. This insures the spike against breakage from side thrust caused by the pressure of the rail. The outside diameter of the threaded portion of the spike is substantially constant throughout its length and the neck 11 is preferably of the same diameter.

In Fig. 2, I have shown the condition of the wood fibers after my spike has been driven into the cross-tie. This is a substantially accurate representation as evidenced by numerous tests which I have made on different kinds of wood. It will be seen that the fibers havenot been materially crushed nor distorted to a point beyond their elastic limit. The ends of the fibers where they contact with the surface of the spike are turned down slightly because of the downward movement of the spike when it is driven into the wood. When my spike is withdrawn from the wood, the hole made by it will gradually close, because the fibers have not materially been crushed or distorted beyond their elastic limit. This elastic condition of the live fibers of the wood, causes a greatly increased frictional hold against the outer surface of the spike, thereby greatly increasin its resistance to pull and also increasing t e life of the hold. Experiments have demonstrated that my' spike may be 'driven into the same hole a number of times, without substantially affecting its holding power. The core 5 is cylindrical for a greater part of its length, and the threads 6 present a uniform diameter to the outside of the spike. These two features, together with the spiral formation of the threads, result in providing a spike which has not only an increased initial resistance to pull, but which, after the initial pull, also maintains a greater resistance during the first as well as subsequent withdrawals from the wood than any of the prior art spikes. My spike is provided with an umbrella-shaped head 13 which is of cylindrical cross-section so that.

it always presents portions of the same surface in contact with the rail at any phase of rotation and also serves to protect the hole in the wood against moisture.

The threads 6 may be of any suitable crosssection, pitch or number. These and other modifications of the details herein shown and described ma be made without departing from the spirit of my invention or the scope of the appended claims; and I d fore, wish to be r 0 not, therelimited to the exact embodiment herein shown and described, the form described being merely a preferred embodiment thereof.

Having thus described my invention, what I claim is:

1. A wood screw formed with a core and a neck, the screw having a substantially uniform outer diameter, a plurality of spirally arranged threads and a. lurahty of interspaced flutes, the flutes eing increased in depth near the lower ends of the threads, and a tapered portion joining the neck portion with the core, the core and the threads being of such a transverse cross-section that they will not materially crush or distort the wood fibers beyond their elastic limits.

2. A Wood screw formed with a core and a neck, the screw having a substantially uni? form outer diameter, a plurality of spirally arranged threads and a plurality of interspaced flutes, the flutes being increased in depth near the lower ends of the threads, a tapered portion joining the neck portion with the core, and a conical point extending from the lower end of the screw.

3. A wood screw having a substantially uniform outer diameter and being tormed with a core, a plurality of spirall arranged threads having their lower ends isposed at right angles to the axis of the screw, a plurality of interspaced flutes, the flutes being increased in depth near the lower ends of the threads, a neck formed at the upper end of the screw, and a tapered portion oining the neck with the core, the core and the threads being of such a transverse cross-section that they will not crush or distort the wood fibers beyond their elasticlimits.

4. A wood screw having a substantially uniform outer diameter and being formed with a core, a plurality of spirally arranged threads of uniform pitch, a plurality of interspaced flutes, the flutes being increased in depth near the lower ends of the threads, a neck formed at the upper end of the screw, and a tapered portion joining the neck with the core, the core and the threads bein of such a transverse cross-section that t ey wi1lnot crush or distort the wood fibers beyond their elastic limits. I

In testimony whereof, I have hereunto signed my name.

FRANK H. WILLIAMS.

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